This is an interesting story that raises some questions. A study found that cell phone use is associated with lower sperm counts in men. Men who used their phones four or more hours per day had the worst counts.

The two theories I’ve come across are that cell phones emit sperm-killing waves and that a cell phone’s heat can lower sperm count.

One thing the media hasn’t been saying much, though, is that the hit is rather minimal. Men who used their phones four or more hours per day had counts averaging 66 million per milliliter, compared to 86 million for men who did not use cell phones. The upper bound for “low sperm count” is 20 million, so the majority of men won’t cross into problem territory from using a cell phone.

For the subjects who did use cell phones, more use was associated with fewer sperm cells. Which prompts the questions: If you have a cell phone, how can using it more often hurt your sperm count? Why wouldn’t the main distinction be between carrying and not carrying a phone?

A source in this story points out that if you use your cell phone four hours a day, that means it’s out of your pocket four more hours. I think this makes the “spermkiller waves” theory unlikely, because more use should mean fewer waves near the testes — unless the waves come out more when the phone is in use and can affect an area, often through the user’s head, several feet away. It’s also possible that people who don’t use their phones as much often leave them home entirely.

The more likely theory is the “heat” one; a study awhile back showed that working with a laptop on your lap can lower sperm count, and its well established that high temperatures in general kill sperm. If you use your phone more, it’s hot when you put it in your pocket or attach it to your belt. If you carry a phone but don’t use it, it doesn’t generate any heat.

A good way to tell would be to repeat the study, looking at whether people put their phones in their pockets or clip them to their belts. Belt clips, I’d hypothesize, minimize the effect of heat by adding two layers of insulation (the case and the pants) and, on average, increasing the distance between the affected area and the phone.

You could also note the number of calls instead of the time spent talking. More calls mean more hot phones in pockets; one four-hour call probably has the same effect as one half-hour one.

Robert VerBruggen blogs at http://robertsrationale.blogspot.com.